Past decades witness an increasing interest in the concept of supervenience, which has traditionally been used as a relation between sets of properties. A set A of properties (called ‘supervenient properties’) is said to supervene on another set B (called ‘subveinent properties’), just in case if B-properties are indistinguishable, then so are A-properties; in other words, agreement in respect of B-properties implies agreement in respect of A-properties. In slogan form, “there cannot be an A-different without a B-difference”. The core idea of supervenience is that fixing subvenient properties fixes its supervenient ones; or equivalently, subvenient properties determine supervenient properties.
The notion of supervenience dates back at least to G. E. Moore’s classical work, where he described some certain dependency relationship between moral and non-moral properties. However, Moore did not use the term ‘supervenience’ explicitly; it was R. M. Hare that introduced the term into the philosophical literature, to characterize a relationship between moral properties and natural properties. Hare stated
First, let us take that characteristic of ‘good’ which has been called its supervenience. Suppose that we say ‘St. Francis was a good man’. It is logically impossible to say this and to maintain at the same time that there might have been another man placed in precisely the same circumstances as St. Francis, and who behaved in them in exactly the same way, but who differed from St. Francis in this respect only, that he was not a good man.
Thanks to Donald Davidson, the term ‘supervenience’ was first introduced into contemporary philosophy of mind, which opened up a new research direction in this area and other branches of philosophy. Donald Davidson used psychophysical supervenience to defend a position of anomalous monism that although the mental supervenes on the physical, the former cannot be reduced to the latter, as he said:
Although the position I describe denies there are psychophysical laws, it is consistent with the view that mental characteristics are in some sense dependent, or supervenient, on physical characteristics. Such supervenience might be taken to mean that there cannot be two events alike in all physical respects but differing in some mental respect, or that an object cannot alter in some mental respect without altering in some physical respect. Dependence or supervenience of this kind does not entail reducibility through law or definition.
It is alleged that every major figure in the history of western philosophy has been at least implicitly committed to some supervenience thesis. For example, Leibniz used the Latin word ‘supervenire’, to state the thesis that relations are supervenient on properties; G. E. Moore stated that “one of the most important facts about qualitative difference · · · [is that] two things cannot differ in quality without differing in intrinsic nature”; David Lewis used a thesis of Humean supervenience to express that the whole truth about a world like ours supervenes on the spatiotemporal distribution of local qualities.
The notion of supervenience is ubiquitous in our daily life. For instance, the aesthetic properties of a work of art supervene on its physical properties, the price of a commodity supervenes on its supply and demand, effects supervene on causes, and the mental supervenes on the physical. According to the chart of levels of existence, atoms supervene on elementary particles, molecules supervene on atoms, cells supervene on molecules, and so on.
Moreover, a number of interesting doctrines and problems can be formulated in terms of supervenience. A paradigmatic example is physicalism, which may be construed as a thesis that “everything supervenes on the physical”. Mereology may be explained as mereological supervenience, i.e., the whole supervenes on its parts. Determinism can be roughly construed as a thesis that everything to the future supervenes on the present, and perhaps past, facts. All of the distinction between internalism and externalism can be characterized by means of supervenience theses. Mind-body problem may be rephrased as to whether the psychophysical supervenience thesis holds, i.e., are psychological properties supervenient upon physical properties?
There are so many distinct formulations for this concept, e.g., individual supervenience, local supervenience, global supervenience, weak supervenience, strong supervenience, similarity-based supervenience, regional supervenience, local-local supervenience and strong-local-local supervenience, multiple domain supervenience, that David Lewis thought of it as an ‘unlovely proliferation’. No matter how different the formulations are, they all conform to the aforementioned core idea of supervenience – that is, fixing the subvenient properties fixes the supervenient properties.
Supervenience has many applications, among which a central use is so-called ‘argument by a false implied supervenience thesis’. It is well known that the reduction of A to B implies the supervenience of A on B; in short, reduction implies supervenience. Thus for one to argue against a reduction thesis, it suffices to falsify the corresponding supervenience thesis. Other applications include characterizing the distinctions between Internalism and Externalism, characterizing physicalism, characterizing haecceitism, and so on.